This invention relates to an improved apparatus for the processing of tar sands. Large deposits of these sands are found as the Athabasca deposits in northern Alberta, Canada. The valuable portion of these deposits occupies about 51/2 million acres and is buried by 0 to 2000 feet of overburden. It has been estimated that these deposits consist of about 600 billion barrels of reserves in place, over 350 billion barrels of recoverable reserves of raw tar sand oil and over 250 billion barrels of upgraded synthetic crude oil (See page 1 of the K. A. Clark Volume edited by M. S. Carrigy, Research Council of Alberta, Oct., 1963). The recoverable reserves estimate is just about equal to the worldwide reserves estimate of conventional oil, 60 percent of which is in the Middle East.
The tar sands are primarily composed of a fine quartz sand having a particle size greater than that passing a 325 mesh screen. The quartz sand is impregnated with a viscous bitumen in quantities of from 5 to 21 weight percent of the total composition. More typically the bitumen content is from 8 to 15 percent. This bitumen is quite viscous--6.degree. to 8.degree. API gravity--and contains typically 4.5 percent sulfur and 38 percent aromatics. Its specific gravity at 60.degree.F. ranges typically from about 1.00 to about 1.06.
In addition to the bitumen and quartz sand, the tar sands contain clay and silt in quantities of from 1 to 50 weight percent of the total composition. Silt is normally defined as material which will pass a 325 mesh screen but which is larger than 2 microns. Clay is material smaller than 2 microns including some siliceous material of that size.
Several basic extraction methods have been known for many years for the separation of bitumen from the sands. In the so-called "cold water" method, the separation is accomplished by mixing the sands with a solvent capable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water with a surface agent added or a solution of a neutral salt in water. The combined mass is then subjected to a pressure or gravity separation.
In the hot water method, the bituminous sands are jetted with steam and mulled with a minor amount of hot water at temperatures in the range of 140.degree. to 210.degree.F. The resulting pulp is dropped into a stream of circulating hot water and carried to a separation cell maintained at a temperature of about 150.degree. to 200.degree.F. In the separation cell, sand settles to the bottom as tailings and bitumen rises to the top in the form of an oil froth. An aqueous middlings layer containing some mineral and bitumen is formed between these layers. A scavenger step may be conducted on the middlings layer from the primary separation step to recover additional amounts of bitumen therefrom. This step usually comprises aerating the middlings as taught by K. A. Clark, "The Hot Water Washing Method", Canadian Oil and Gas Industries, 3, 46 (1950). These froths can be combined, diluted with naphtha and centrifuged to remove more water and residual mineral. The naphtha is then distilled off and the bitumen is coked to a quality crude suitable for further processing.